1. Field of the Invention
This invention relates generally to a method and apparatus for demixing aqueous solutions and, more particularly, it relates to a method and apparatus for demixing aqueous solutions which enhances the demixing rate by the application of acoustic energy to the aqueous solution.
2. Description of the Prior Art
Methods for the separation, concentration, and purification of biological products such as proteins, enzymes, viruses, cells, and other biological materials from fermentation and other cell culture media are well known in the art. Methods currently in use to separate two-phase aqueous systems at equilibrium include gravity settling, centrifugation, chromatography, and electrokinetic demixing. These methods have significant disadvantages that make these methods unsuitable for large-scale use.
In an aqueous two-phase systems method, a dissolved chemical product is extracted by partitioning the dissolved chemical product into one of the two immiscible liquid phases (aqueous solutions of two polymers or a polymer and a salt). Aqueous two-phase systems require the phases to be mechanically mixed and then allowed to separate. Since these aqueous phases are characterized by high viscosities, low interfacial tensions, and similar densities between the two liquid phases, a slow demixing of the liquid phases occurs. Due to the slowness of the separation and the cost of the phase-forming chemical components required, the aqueous two-phase systems method has not been accepted for wide industrial application.
Concerning the other methods of separation, demixing by gravity settling is very slow. Centrifugation demixing is prohibitively expensive on a large scale. Electrokinetic demixing requires the use of special equipment and the addition of salts to the system. Therefore, from the economics point of view, due to the capital equipment and operational costs, centrifugation demixing becomes prohibitively expensive and impractical on a large scale and electrokinetic demixing requires fabrication of special equipment and chemical additions, such as salts, to the aqueous two-phase system.
Efforts have been made to overcome the inherent shortcomings of the demixing separation methods of the prior art which are developed for solidliquid systems and not liquid-liquid systems. The Trampler et al, U.S. Pat. No. 5,527,460, describes an ultrasonic resonance wavefield apparatus and method for separation of mammalian cells from a liquid medium. The transducer and mirror of the Trampler et al patent are positioned parallel to each other producing sonification in a horizontal direction. Since the gravity vector is perpendicular to the sonification, the standing resonance wavefield of the Trampler et al patent facilitates the sedimentation of the mammalian cells from the liquid medium.
Accordingly, there exists a need for a method and apparatus for demixing aqueous solutions which enhances the demixing rate of the mixed liquid phases that are at equilibrium with each other by the application of acoustic energy. Additionally, a need exists for a method and apparatus for acoustically demixing aqueous solutions which has reduced capital and operational costs as compared to other demixing methods and processes.